The present invention relates to mobile radiotelephone systems and more particularly to call priority in such systems.
A constant challenge facing mobile telephone engineers has been to provide a level of telephone service virtually indistinguishable from that available at a hard-wired telephone extension while operating under a fundamentally different set of conditions and assumptions. One service available in the "wire bound" telephone network has been user priority. In accordance with such priority, a call may, due to the category of a subscriber or the number dialed, be given priority when assigning resources in the network such as registers, cord circuits, trunk lines, paths through a selector, etc. Such a priority scheme becomes insufficient, however, in the fundamentally different mobile radio telephone environment.
Priorities arise from the necessity to manage competition for a limited resource. In a cellular mobile radiotelephone, competition occurs for making an access, being paged, and having a good voice channel or queuing (waiting) the least amount of time for one, among other things. These types of resource competitions should be managed effectively in the cellular mobile radiotelephone system according to the subscriber's own priority (urgency) to use the system/resource, and the system's priority to service the subscriber. Because to a large extent what is good for the subscriber is also good for the system, the system's priority should be a function of the subscriber's priority as well as relevant call and network specifics.
Call priority may be described as handling a call differently from similarly situated calls so as to perceptibly increase the quality of service of that call as compared to the other calls. High quality service may be described as: 1) certain call completion 2) with minimum delay 3) with good sound reproduction at both ends of the connection (or, in the case of data transmission, errorless transmission, in both directions in the case of duplex data exchange).
Certain call completion depends on the number of available circuits, minimum delay depends on quickly locating the mobile and then (possibly) routing efficiency and lack of congestion, and good sound reproduction depends on low-distortion transmission channels. In the wire-bound network, because of the vast size and advanced development of the network, at least in United States, certain call completion is rarely a problem. Furthermore, most lines are conditioned and tested to guarantee satisfactory sound reproduction.
In a mobile radiotelephone network, on the other hand, the number of available channels is much more limited, in part because the radio-frequency spectrum is a scarce resource and only a limited portion of that spectrum has been allocated to radiotelephone use. Furthermore, radio channels, even assuming fixed base stations, unavoidably vary in quality according to atmospheric conditions, and when the relative position of stations is time-varying (possibly quite rapidly) as in a mobile radiotelephone network, the variability of channel quality greatly increases. The main contributors to the variability of channel quality are co-channel and adjacent channel interference, and noise. Radio channels obviously cannot be conditioned in the same manner as wire lines.
An object of the present invention, therefore, is to provide call priority in a mobile radiotelephone network. More particularly, an object of the present invention is to provide in a mobile radiotelephone network for handling priority-designated calls differently from other concurrent calls so as to perceptibly increase the quality of service of the priority call by, to the extent possible, assuring call completion with good sound reproduction. Preferably, call completion is accomplished with minimal delay.